Gaseous electric discharge device



y 1935 G. GAIDIES GASEOUS ELECTRIC DISCHARGE DEVICE Filed Oct. 15, 1955 VENTOR Patented July 7, 1936 UNITED STATES PATENT OFFICE Georg Gaidies, Berlin-Pankow, Germany, asslgnor to General Electric Company, a corporation of New York Application October 15, 1935, Serial No. 45,139 In Germany October 26, 1934 3 Claims. (01. 176-126) The present invention relates to gaseous electric discharge devices generally and more particularly the invention relates to electrode structures for such devices.

5 Thermionic electrodes of the type heated directly by the discharge current and consisting of a tungsten filament connected to a current lead and wrapped around a rod consisting of or comprising a material having high electron emissivity are useful in gaseous electric discharge devices operating at commercial voltages, such as 110 or 220 volts, and with a discharge current greater than about 100 milliamperes. The use of this type of electrode in gaseous electric discharge devices, such as gaseous electric discharge lamps, operating on like voltages and with a discharge current of less than about 100 milliamperes, such as a discharge current of about milliamperes. is not practicable as the current 20 flowing through the electrode is not of suflicient magnitude to heat the electrode to the temperature at which the discharge device operates most efiiciently.

The object of the present invention is to provide a thermionic electrode of the directly heated type useful in gaseous electric discharge devices generally and particularly in gaseous electric discharge lamp's operating on the usual commercial voltages and with a discharge current of 3 less than about 100 milliamperes. Still further objects and advantages attaching to the device and to its use and operation will be apparent to those skilled in the art from the following a particular description. In accordance with these objects the new electrode comprises a metal filament, such as a tungsten filament, wrapped around a rod of highly electron emissive material, such as an alkaline earth metal, and a tube consisting of 40 the oxide of an alkaline earth metal, such as barium oxide, surrounding said rod and said filament and in contact with said filament to form a unitary electrode structure. The oxide tube projects beyond the filament and the rod in the direction of the discharge incident at the electrode. When desired, the oxide tube is surrounded by a 'metal tube electrically insulated and separated a small distance therefrom. The electrode is mounted in the discharge device with one end of the oxide tube opening in the direction of the discharge path. The oxide tube reduces the radiation of heat from the tungsten filament and the rod, which are heated by the discharge current, and guides the gasecos electric discharge incident at the electrode to the small surface at the end of the highly electron emissive rod facing the discharge path. The end of the rod is heated to a high temperature by the voltage drop thereat and the discharge current flow therethrough and emits a 5 heavy stream of electrons. The parts of the alkaline earth metal oxide tube adjacent the end of the rod facing the discharge path are heated to a high temperature by the heat conducted from the filament and by the heat from 10 the gaseous electric discharge and the oxide breaks down to form oxygen and metal. The alkaline earth metal at the end of the tube also emits electrons. The metal tube surrounding the electrode reduces the radiation of heat from 15 the thermionic electrode which operates at a higher temperature and emits a heavier stream of electrons than would be the case were the metal tube omitted.

The heavy stream of electrons emitted by 20 the electrode makes possible the easy starting and eflicient operation of gaseous electric discharge devices operating on the usual commercial voltages and at discharge currents of less than milliamperes. 25

In the drawing accompanying and forming part of this specification an embodiment of the invention is shown, in which Fig. 1 is a side elevational view of a gaseous electric discharge lamp having electrodes made in accordance with the present invention, and

Fig. 2 is a side elevational partly sectional view of one end of the discharge lamp illu strated in Fig. l and illustrating in detail the new electrode. 35

Like numbers denote like parts in both. the figures.

Referring to Fig. 1 of the drawing, the gaseous electric discharge lamp comprises a tubular container I having one of the new directly heated 40 electrodes sealed therein at each end thereof and having a discharge conducting gaseous atmosphere therein, such as a rare gas, a mixture of rare gases, 2. metal vapor, a mixture of metal vapors, or a mixture of rare gas and metal va- 45 por. Said container 1 has therein neon mixed with a small percentage argon at a pressure of about 1 to 10 mm., when desired.

The electrode is shown in detail in Fig. 2

of the drawing and consists of a helically coiled 50 I to support said filament i in said container I. The longitudinal axis of the helically coiled filament l is coincident with the longitudinal axis of the tubular container I. Said filament O is wrapped around'a rod 1 of material having high electron emissivity, such as an alkaline earth metal, and firmly supports said rod I. When desired, the rod I consists of barium, a mixture of barium and strontium, or a mixture of alkaline earth metal and the oxide thereof.

A tube 8 closely surrounds the coiled filament 6 and the rod 1 and is supported by said filament i. The ends of the tube 8 extend beyond said rod 1 and said filament 6 in both directions, though it will be understood, of cause, that only the end of the tube I in the direction of the discharge incident at the electrode extends beyond said filament and said rod 1 when desired. Said tube 8 consists of the oxide of an alkaline earth metal or a mixture of the oxides of such metals. Preferably the tube 8 consists of barium oxide. As pointed out above the tube 0 reduces the heat losses from the electrode elements I and 8 and guides the gaseous electric discharge incident at the electrode to the end of the rod I where said discharge terminates. The end of the rod 1 is heated to an electron emitting temperature by the voltage drop thereat and by the discharge current fiow therethrough during the operation of the gaseous electric discharge lamp and the end parts of the tube 8 adjacent the discharge supporting end of the rod 1 are likewise at an electron emitting temperature during the operation of the lamp.

A metal tube 9 surrounds the tube 8 and is supported by the rod Ill attached thereto and fused into said pinch part 3. It will be noted that the tube 9 is not connected to the filament I. The tube 9 reduces the heat losses from the electrode elements 6, I and I and intercepts the sputtered particles of material from the electrode 6, I, 8 to prevent blackening of the inner wall of the container I.

The prolific emission of electrons characteristic of new electrode makes the electrode useful not only in gaseous electric discharge lamps operating with discharge currents as low as 20 milliamperes and on commercial voltages but also in voltage dividers since fluctuations in current strength are minimized by confining the terminus of the gaseous electric discharge to one part of the electrode.

While we have shown and described and have pointed out in the annexed claims certain novel features of the invention, it will be understood that various omissions. substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:-

1. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, each of said electrodes comprising a metal filament wrapped around a rod comprising alkaline earth metal and a tube of alkaline earth oxide closely surrounding said filament and said rod, said rod and said oxide tube being axially supported in said container by said filament.

2. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, each of said electrodes comprising a metal filament wrapped around a rod comprising alkaline earth metal and a tube of alkaline earth oxide closely surrounding said filament and said rod, said rod and said oxide tube being axially supported in said container: by said filament, said tube extending beyond said filament in the direction of the discharge path in said container.

3. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, and a metal tube mounted therein, each of said electrodes comprising a metal filament wrapped around a rod 40 by said filament, said tube extending beyond 46 said filament in the direction of the discharge path in said container, said metal tube surrounding said oxide tube.

' GEORG GAIDIKS. 

